1. Field of the Invention
The present invention relates to phase shifters and wireless communication devices, and more particularly, the present invention relates to a phase shifter used in a microwave band or a millimeter wave band and a wireless communication device using the same.
2. Description of the Related Art
Generally, a base station, which is a wireless communication device, includes a phase shifter for adjusting a phase to achieve a desired one in order to enable a common-amplification amplifier to continuously change the phase of a high-frequency signal.
FIG. 10 shows a conventional phase shifter used in a microwave band. A phase shifter 70 includes an input terminal 71, an output terminal 72, control terminals 73, 74, 75, 76 for controlling a transmission line through which the high-frequency signal passes, transmission lines 77 and 78 having different passing phases, and field-effect transistors (hereinafter, referred to as FET) 79, 80, 81, 82 for switching between conduction and insulation across the input and the output.
In the conventional phase-shifter 70, applying 0V to the control terminals 73 and 74 of the FETs 79 and 80 turns on the FETs 79 and 80. Applying a voltage, which is a pinch-off voltage or below, e.g. xe2x88x925V, to the control terminals 75 and 76 of the FETs 81 and 82 turns off the FETs 81 and 82. This allows the high-frequency signal input from the input terminal 71 to pass the transmission line 77. On the other hand, turning off the FETs 79 and 80 and turning on the FETs 81 and 82 allow the high-frequency signal to pass the transmission line 78. When the signal passes, since there is phase difference between the transmission line 77 and the transmission line 78, a phase difference is generated between the two states. By controlling the phase in this manner, the phase of the high-frequency signal is obtained.
However, there is a problem in that, since the foregoing conventional phase shifter has a plurality of transmission lines having different phases that are switched via FETs, the phase cannot be controlled in a continuously variable manner.
In addition, since FETs included in each of the transmission paths are required to vary the multiple phases, the number of components is increased. This also causes problems such as complications in the construction of the phase shifter itself, an increase in the size of the phase shifter, and an increase in the manufacturing cost of the phase shifter.
In order to overcome the problems described above, preferred embodiments of the present invention provide a portable phase shifter as well as a communication device for accurately and easily controlling the phase in a continuously variable manner.
According to a first preferred embodiment of the present invention, a phase shifter includes a comb-line defined by first and second transmission lines electromagnetically coupled with each other and a plurality of variable-capacitance diodes respectively connected to the first and second transmission lines defining the comb-line wherein one end of the first transmission line is connected to an input terminal of the phase shifter, one end of the second transmission line is connected to an output terminal of the phase shifter, and the variable-capacitance diodes are connected between the other ends of the first and second transmission lines and the corresponding grounds.
In the phase shifter according to the first preferred embodiment of the present invention, since variable-capacitance diodes are connected between the other ends of first and second transmission lines constituting a comb-line and the corresponding grounds, the capacitances of these variable-capacitance diodes can be variably controlled by controlling the voltages applied to these variable-capacitance diodes. As a result of this, the impedances of the variable-capacitance diodes can be controlled in a variable manner and the phase of the high-frequency signal transmitted from the input terminal to the output terminal of the phase shifter via the comb-line can be controlled in a variable manner.
Since the comb-line and the variable-capacitance diodes constitute the phase shifter, the construction of the phase shifter is greatly simplified. As a result of this, the phase shifter can be miniaturized and, in addition, the manufacturing cost thereof can be decreased.
The variable-capacitance diodes may be connected in parallel with resistors.
Since the variable-capacitance diodes are connected in parallel with resistors, the phase can be varied while the reflection coefficient is maintained. Therefore, in the phase shifter, the phase can be varied while the change in the amplitude can be prevented.
A phase shifter may further include a ceramic substrate obtained by laminating a ceramic plurality of sheet layers, wherein a strip electrode, defining the comb-line, is incorporated in the ceramic substrate and the variable-capacitance diodes are mounted in the ceramic substrate.
Since the ceramic substrate obtained by laminating a plurality of ceramic sheet layers is provided and copper strip electrodes constituting the comb-line are incorporated in the ceramic substrate, a xe2x80x9cwavelength reduction effectxe2x80x9d caused by the ceramic substrate and reduction in loss due to use of copper allow the phase shifter to be adapted for use in a high-frequency band of 1 GHz or above.
According to a second preferred embodiment of the present invention, a phase shifter includes a first comb-line defined by first and second transmission lines electromagnetically coupled with each other, a second comb-line defined by third and fourth transmission lines electromagnetically coupled with each other, and variable-capacitance diodes each connected to the third and fourth transmission lines defining the second comb-line wherein one end of the first transmission line is connected to an input terminal, one end of the second transmission line is connected to an output terminal, the variable-capacitance diodes are connected between ends of the third and fourth transmission lines and the corresponding grounds, and the other end of the first transmission line and the other end of the second transmission line are connected to the other end of the third transmission line and the other end of the fourth transmission line, respectively.
Since the variable-capacitance diodes are connected between the other ends of the third and fourth transmission lines constituting the second comb-line and the corresponding grounds, the capacitances of these variable-capacitance diodes can be variably controlled by controlling the voltages applied to the variable-capacitance diodes. As a result of this, the impedances of the variable-capacitance diodes can be variably controlled and the phase of the high-frequency signal transmitted from the input terminal to the output terminal of the phase shifter via the first and second comb-lines can be variably controlled.
Since the first and second comb-lines and the variable-capacitance diodes constitute the phase shifter, the construction of the phase shifter is simplified. As a result of this, the phase shifter is greatly miniaturized and, in addition, the manufacturing cost thereof is greatly decreased.
In this phase shifter, the variable-capacitance diodes may be connected in parallel with resistors.
Since the variable-capacitance diodes are connected in parallel with the resistors, the phase can be varied while the reflection coefficient is maintained. Therefore, in the phase shifter, the phase can be varied while the change in the amplitude is prevented.
A phase shifter may further include a ceramic substrate obtained by laminating a plurality of sheet layers including ceramic material, wherein, strip electrodes, defining the first and second comb-lines, are incorporated in the ceramic substrate and the variable-capacitance diodes are mounted in the ceramic substrate.
Since the ceramic substrate obtained by laminating a plurality of ceramic sheet layers is provided and the copper strip electrodes constituting the comb-line are incorporated in the ceramic substrate. Therefore, the xe2x80x9cwavelength reduction effectxe2x80x9d caused by the ceramic substrate and the reduction in loss due to use of copper allow the phase shifter to be adapted for use in the high-frequency band of 1 GHz or above.
Since the first and second comb-lines are arranged so as to be overlapped in the vertical direction of the ceramic substrate, the mounting area of the phase shifter is greatly decreased.
According to a third preferred embodiment of the present invention, a wireless device includes a phase shifter according to any one of the above preferred embodiments and related modifications.
Since the portable phase shifter is used, a small base station having a preferable transmission characteristic can be realized.
Other features, elements, characteristics and advantages of the present invention will become apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.